Carburetor



Oct. 11, 1932.

1929 2 Sheets-Sheet 1 Fab Oct. 11, 1932. D. FIRTH CARBURETOR Fiied Aug. 12. 1929 2 Sheets-Sheet 2 4Jmzzd72rf/7. @l W 5.

Patented Oct. 11 1932 DAVID FIRTH, 01' FLINT, IICHIGAN, ASSIGNOB '10 MARVEL omnmm'mn co, or

FLINT, MICHIGAN, A CORPORATION OF ILLINOIS cmuam'on Application filed August 12, 1929. Serial No. 385,884.

This invention relates to carburetors for internal combustion engines and has special reference to carburetors embodying auxiliary air valves wherein the transposition from idling to partial load is ordinarily accompanied by a lean point in the mixture proportioning.

It is an object of my inventionto produce a carburetor of the auxiliary air valve type wherein the idling adjustment may be such that the air valve is kept as close to its seat as possible, as such an arrangement gives a more positive idling and a. firmer acceleration; i. e. fluttering or surging is reduced or eliminated during acceleration. In order to carry the air valve approximately on its seat, a small orifice or a restricted flow in the low speed nozzle must be used, but such a restriction produces a very pronounced leanness just ofi idle, or at 600 to 800 R. P. M. part throttle. The present invention relates to means for overcoming this leanness at part throttle without affecting the idling, power,

and economy ranges.

It is also an object of this invention to provide an improved and simplified carburetor of the classdescribed having an improved idling performance accompanied by an economical part load range and a maximum power range wherein the transition between idling and part load and full power is accomplished by means of a single automatically operated fuel metering valve controlling the supply of fuel to both the low and high speed nozzles.

Other and further important objects of this invention will be apparent from the disclosures in the specification and the accompanying drawings.

This invention (in a preferred form.) is illustrated in the drawings and hereinafter more fully described.

()n the drawings: 7

Figure 1 is an elevation of a carburetor partly broken away to show features of this invention as applied thereto.

Figure 2 is a fragmentary'section on the line Ill-H of Figure 1.

Figure 3 is a fragmentarysection on the" line IIIIII of Figure 2.

Figure 4 is an elevation similar to Figure 1, wherein the section also shows the high speed nozzle fuel supply passage together with a slightly opened throttle and air valve.

Figure 5 is similar to Figure 4 and discloses the results of a further opening movement of the throttle and air valve.

As shown on the drawings:

The carburetor chosen for, illustrative purposes has an air inlet '10, and a mixture discharge outlet 11, which is connected to a manifold riser 12 containing a throttle valve on a shaft 13 operated by a lever 14:. A flap air valve 15 is mounted between the air inlet and the mixture outlet and is so positioned as to have a Venturi effect on a high speed nozzle 16 discharging adjacent the free edge of the valve. The air valve is pivotally mounted on a shaft 17 and is urged towards its closed position against the wall of the mixture outlet by means of a strut 18 backed by a spring 19 within an adjustable chamber 20 which is screwed in or out to vary the spring pressure. This adjustment is for idling purposes as it is desirable to keep the air valve as close to its seat as possible for idling, such an adjustment giving a more positive idle and reducing or eliminating valve flutter upon acceleration. While it forms no part of the present invention, it may be noted that the chamber 20 acts as a dash pot to assist in preventing flutter of the air valve due to suction impulses set up by the engine. 1

The carburetor has the usual float chamber- 21 together with float mechanism (not shown) for maintaining a constant level of fuel therein. This chamber 21 supplies fuel to the high speed nozzle 16 as well as a low speed nozzle 22 which is located in a primary Venturi 23 forming an idling mixture passage to one side of the air valve.

When the foregoing nozzle structures are supplied with fuel directly from the -float bowl or chamber, the nozzles must be so calibrated that the high speed nozzle supplies a suitable mixture for average operating conditions, while the low speed or idling nozzle is calibrated for idling with the air valve closed. With such an arrangement, at a slight opening of the air valve, corresponding to an engine speed of about 600 to 800 R. P. M., a very pronounced leanness results because of the additional air passing the air valve, which air does not draw out a propor:

' tional amount of fuel from the high speed open air valve.

nozzle due to the height thereof, so that the proper mixture delivered by the primary venturi thinned out by the extra practically uncarbureted air passing the slightly Moreover, when the hlgh speed nozzle is calibrated for best results under normal conditions the full power of the engine is not available because maximum power output requires a richer mixture. The

resent invention overcomes the two drawhacks mentioned above by the provision of a combined valve and metering pin, to be hereinafter described, controlling the supply of fuel to both nozzles, which are changed in calibration from that ordinarily employed so that the maximum delivery of the high speed nozzle is suflicient to form a rich mixture for maximum power while the low speed or idling nozzle is increased in size sufficiently to over- ;come the leanness just off the idling position as hereinbefore mentioned. With such en- I larged nozzles it becomes necessary to restrict or meter the fuel supplied thereto under normal operating conditions in order to obtain an economical driving range.

For idling with the air Valve as close to its seat as ossible a relatively small flow of fuel to t 1e low speed nozzle is desirable. In order to obtain control of this small flow, a fuel passage 24 leads from the float chamber to a meterlng chamber 25 at the bottom of a vertical passa e 26 leading to the low speed. 'nozzle. The ow is metered by an externally adjustable needle valve 27 cooperatin with an orifice plug 28 between the chamber 25 and the passage 26, the valve 27 being set to limit the fuel flow for optimum conditions at a strictly idling speed of the engine.

7 In order to supply excess fuel to the low speed nozzle when it is desired to have the calibration of the nozzle itself control the fuel delivery for conditions of operation just off throttle, or at an engine speed of 600 to 800 RP. M., in which range a pronounced leanness would otherwise be evident; a supplemental fuel supply is provided. This comprises a passage 29 opening into a well 30 and flowing through an orifice plug 31 about the stem 32 of a metering rod 33 and through a second orifice plug 34; which forms a valve seat for the tapered end 35 of the metering rod 33-; into a chamber 36 from which an inclined. passage 37 delivers fuel to the passage 26 above the plug 28. Thus when the end 35 of the metering rod is off its seat in the plug 34 a secondary passage for fuel is provided which leads directly to the low speed nozzle and supplements the quantity of idling fuel flowing past the idling meter ing valve 27.

The annular orifice formed between the plug 31 and the shank of the metering rod 33 is proportioned to provide an economical sulting in an increased flow of fuel which is then metered by the calibrated outlet of the high speed nozzle.

With the foregoing described arrangement the low and high speed nozzles both cooperate with a single fuel supply arrangement, the metering rod forming a combination of a valve for the low speed nozzle supply and as a metering pin for the flow of fuel to the high speed nozzle in the normal driving range, above which the pin is withdrawn from the orifice 31 and the high speed nozzle outlet governs the fuel flow from then on.

In order to operate the metering rod to accomplish the described results, I provide a cam 39 on the throttle shaft 13 which engages one end 40 of a bell crank lever pivoted at 41. The other end 42 of the lever engages a collar 43 on the threaded portion of rod 33, the collar acting under an adjustable nut 45 to lift the rod 33 which projects into the well 30 is arranged and carries the metering rod shank 32 on its lower end. The rod carries a flange 46 forming a spring seat for a spring 47 which maintains the bell crank in contact with the cam.

The cam 39 is so proportioned and positioned relative to the bell crank lever and the throttle that when the latter is closed for idling, the metering rod end 35 is seated in the orifice plug 34, cutting off the secondary supply of fuel to the idling or low speed nozzle as shown inFigure 1. Upon a very slight opening movement of the throttle the camment of the bell crank lever by the cam 39,

lifting the metering pin 33 out of the upper orifice plug 31 resulting in an increased supply of fuel to the high speed nozzle which then serves to meter the fiow of fuel for maximum power for which a richer mixture is desirable.

It will thus be seen that I have invented an improved and simplified carburetor of the air valve type wherein undue leanness of the mixture, due to a slight opening of the air valve is compensated for and wherein the same. compensating fuel metering device serves to richer mixture for maximum power near wide open throttle conditions.

I am aware that many changes may be made and numerous details of construction may be varied through a wide range without departing from the principles of this invention, and I, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

1. In a carburetor, a mixing chamber, an air inlet leading thereto, an air valve interposed between said air inlet and said mixing chamber, a high speed nozzlepositioned between said air inlet and said air valve, a low speed nozzle, a fuel reservoir, a conduit connected to said fuel reservoir and said low speed nozzle to supply fuel to the low speed nozzle sufficient for idling requirements, another conduit connecting said fuel reservoir with said high speed and said low speed nozles to supply a relatively unlimited amount of fuel to said low speed nozzle, a member in said another conduit having an orifice, a needle valve adapted to open and close the orifice whereby to control flow of fuel in said low speed nozzle and to simultaneously meter the fuel supply to said high speed nozzle.

2. In a carburetor, a mixing chamber, an air inlet leading thereto, a suction operated air valve interposed between said air inlet and said mixing chamber, a high speed nozzle positioned between said air inlet and said air valve, a low speed nozzle, a fuel reservoir, a conduit connected to said fuel reservoir and said low speed nozzle to supply fuel to the low speed nozzle suflicient for idling requirements, another conduit connecting said fuel reservoir with said high speed and said low speed nozzles to supply a relatively unlimited amount of fuel to said low speed nozzle, a member in said another conduit having an orifice, a needle valve adapted to open and close the orifice whereby to control flow of fuel to said low speed nozzle and to simultaneously meter the fuel supply to said high speed nozzle.

3. In a carburetor, a mixing chamber, an air inlet leading thereto, an air valve interposed between said air inlet and said mixing chamber, a high speed nozzle positioned between said air inlet and said air valve, a low speed nozzle, a fuel reservoir, a conduit connected to said fuel reservoir and said low speed nozzle tosupply fuel to the low speed nozzle sufiicient for idling requirements, an-

other conduit connecting said fuel reservoir with said high speed and said low speed nozzles to supply'a relatively unlimited amount of fuel. to said low speed nozzle, a member in said another conduit having a calibrated orifice, a second member in said another'conduit having an orifice therein larger than the first named orifice, a pin extending in said second member movable to close and open said first namedorifice whereby to control flow of fuel to said low speed-nozzle and to simultaneously meter the fuel supply to said high speed nozzle.

4. In a carburetor, a mixing chamber, an air inlet leading thereto, an air valve interposed between said air inlet and said miX ing chamber, a high speed nozzle positioned between said air inlet and said air valve, a low speed nozzle, a fuel reservoir, a conduit connected to said fuel reservoir and said low speed nozzle to supplyfuel to the low speed nozzle sufiicient for idling requirements, another conduit connecting said fuel reservoir with said high speed and said low speed nozzles to supply a relatively unlimited amount of fuel to said low speed nozzle, a member in said another conduit having an orifice, a needle valve adapted to open and close the ori-. fice whereby to control flow of fuel to said low speed nozzle and to simultaneously meter the fuel supply to said high speed nozzle, a 1 throttle, a cam carried by said throttle, and means operated by said cam for operating said needle valve in predetermined relationship to said throttle. I

5. In a carburetor, a mixing chamber, an air inlet leading thereto, an ear valve interposed between said air inlet and said mixing chamber, a high speed nozzle, a low speed nozzle, a fuel reservoir, a conduit connect- 1G3 ing said reservoir and said low speed nozzle to supply fuel to the low speed nozzle, sufficient for idling requirements, another conduit connecting said reservoir with said high speed nozzle and said low speed nozzle, a member in said another conduit having an orifice, a metering pin movable extending in said member to meter the fuel entering said another conduit, a second member in said another conduit having an orifice, said sec- 0nd member being interposed between said first member and said low speed nozzle in spaced opposed relation to said first member, said metering pin being movable adapted to close and open the orifice of said second me'mber to thereby control flow of fuel to said low speed nozzle, said another conduit pro- I viding means to supply a relatively unlimited fuel supply to said low speed nozzle, a throttle, and means connecting said throttle and said metering pin for cooperative movements.

In testimony whereof I have hereunto subscribed my name.

DAVID FIRTH. 

